Stopping Fatal Heart Attacks With Fish
Eating foods rich in omega-3 fatty acids may reduce therisk of
dying from coronary heart disease.
A line of research cast in
the late 1970s has spawned a wealth of knowledge about a beneficial
type of fat: omega-3 fatty acids.
Found in fish and some plant products, these fats have been shown
to lower the risk of sudden death from heart attacks in people
with CHD. They may also benefit people at risk for CHD.
Omega-3 Fatty Acids?
The three major types of highly unsaturated
omega-3 fatty acids are eicosapentaenoic acid (EPA), docosahexaenoic
and alpha-linolenic acid (ALA). The only sources of EPA and DHA
are fish (particularly fatty fish) and fish oils. (For a list
of fish high in EPA and DHA, see the inset box on the opposite
page.) ALA is found in certain plant and plant products, such
as canola, soybeans, walnuts, and flaxseed, as well as the oils
of these plants. Evidence is mounting that EPA and DHA can protect
the heart; the data for ALA are not as strong.
Research into the heart benefits of omega-3 fatty
acids began in the 1970s and 1980s when studies suggested that
ate copious amounts of fish—for example, Japanese living
in fishing villages and Greenland Eskimos—tended to have
lower rates of atherosclerosis and heart attacks than Americans.
Researchers hypothesized that the omega-3 fatty acids in fish
might be responsible for this benefit.
A number of randomized
clinical trials have examined the heart benefits of omega-3 fatty
acid consumption in people diagnosed
with CHD. A meta-analysis of these trials published in the American
Journal of Medicine in 2002 reported that, in 11 randomized trials
containing 15,806 people, omega-3 fatty acid-enriched diets or
supplements decreased the risk of fatal heart attacks and sudden
death from cardiac arrest by 30% and overall deaths by 20% compared
with control diets or a placebo. However, the risk of nonfatal
heart attacks was not significantly reduced.
How Do Omega-3 Fatty Acids Work?
Many experts suspect that the
main mechanism by which omega-3 fatty acids reduce the risk of
sudden death from CHD is by decreasing
the heart’s susceptibility to dangerous arrhythmias (irregular
heart rhythms). The heart can begin to beat irregularly when
it is subjected to stress, for example when it is not getting
enough oxygen. These irregular heartbeats may lead to fatal ventricular
fibrillation. Omega-3 fatty acids are incorporated into the membranes
of cells in the heart, where they may stabilize the heart’s
Omega-3 fatty acids appear to have other beneficial effects
on the heart. There is good evidence that they help reduce blood
triglyceride levels. There is also some evidence, albeit less
certain, that omega-3 fatty acids reduce the risk of blood clots,
the growth of plaque in the arteries, high blood pressure, and
inflammation, all of which contribute to atherosclerosis. They
also appear to improve the function of blood vessels.
Enough Omega-3 Fatty Acids
The average person in North America
eats fish about once every 10 days and consumes about 1,600 mg
of omega-3 fatty acids daily
(about 200 mg of EPA and DHA combined and 1,400 mg of ALA). By
contrast, the American Heart Association recommends that people
not diagnosed with CHD eat fish, particularly those high in omega-3
fatty acids, at least twice weekly in addition to oils, nuts,
and seeds high in ALA. For people who already have CHD, the organization
recommends about 1,000 mg of EPA plus DHA per day from fatty
fish, fish oil supplements, or a combination of both.
fish you eat is prepared may determine how well it protects against
fatal CHD. In a study published in Circulation in March
2003, researchers found that people who ate broiled or baked
fish three or more times per week had a 49% lower risk of fatal
CHD and a 58% lower risk of death from a CHD-related arrhythmia
than people who ate fish less than once a month. But people who
ate fried fish or fish sandwiches experienced no reduced rate
of CHD. Blood levels of omega-3 fatty acids were significantly
higher in the people who consistently ate broiled or baked fish
than in those who ate fried fish or fish sandwiches regularly.
The researchers suggest that frying may reduce the omega-3 fatty
acid content of fish. Another possible explanation is that the
type of fish typically fried or used in fish sandwiches is not
rich in omega-3 fatty acids.
Although current recommendations
are that omega-3 fatty acids should preferably be obtained through
food, some people may prefer
fish oil supplements instead of, or in addition to, fish. Always
consult your physician before beginning to take a fish oil supplement.
Also, check the label of the supplement to determine its EPA
and DHA content. A 1,000-mg fish oil capsule usually contains
about 180 mg of EPA and 120 mg of DHA. This means that a person
may have to take two to three capsules daily, in addition to
eating fish regularly, to meet the American Heart Association’s
recommendation for omega-3 fatty acid intake for people with
Unfortunately, because the U.S. Food and Drug Administration
does not regulate these supplements, different batches of the
same brand may not contain the same levels of active ingredient.
In addition, the content of EPA and DHA may not match the amount
indicated on the label.
Potential Side Effects
One of the main concerns associated with
eating large quantities of fish is that some species contain
high levels of pollutants
like methylmercury and polychlorinated biphenyls (PCBs). One
recent study suggested that methylmercury exposure may increase
the risk of CHD, while another found that methylmercury did not
increase the risk.
Given the current data, experts say that the
potential benefits of eating fish outweigh the possible risks
for middle-aged and
older men and for postmenopausal women. If you are concerned
about exposure to pollutants, try to eat a variety of fish and
avoid species like shark, swordfish, king mackerel, and tilefish.
Fresh tuna is also high in methylmercury, and large amounts should
probably be avoided; but canned tuna appears to be relatively
Fish oil supplements are mercury free, but they can cause
side effects such as nausea, gastrointestinal upset, and a fishy
High intakes of omega-3 fatty acids from fish oil supplements
(more than 3,000 mg per day of EPA plus DHA) are associated with
an increased risk of bleeding and should be taken only under
a doctor’s supervision.
Good Sources of Omega-3 Fatty Acids
(EPA and DHA)
Type of fish
per 3 oz. serving
Source: United States Department of Agriculture.